Chernobyl: Flying low and slow

Because so many novice pilots stall, crash and burn while flying low andslow -- on takeoff and landing, mostly, with flaps and wheels down -- FAAexaminers require pilots to demonstrate their ability to fly their aircraftat minimum controllable airspeed, right on the edge of a stall.

Of course, not being complete idiots, FAA examiners do not allow thepilot to demonstrate those abilities unless the aircraft is up severalthousand feet above the ground, so that if the pilot does stall and theaircraft quits flying and begins to fall like a rock there is time forsomeone in the aircraft to recover from the stall -- get it flying again --before it crashes and burns.

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What the operators of Chernobyl Power Plant Unit 4 -- who apparentlywere complete idiots -- were trying to do was to operate their nuclearreactor right on the edge of a stall. But when their reactor stalled, therewas no time to recover.

In any nuclear power plant, a fraction (10-15 percent) of theelectricity generated is needed to operate the plant itself, whether atfull power or zero power. Since when operating at zero power no electricityis being generated, the electricity needed to operate the plant itself atzero power has to be imported. What the Unit 4 operators were attempting todo was to run the plant at the bare minimum power level to keep the plantidling.

Chernobyl-style nuclear plants -- called RBMKs -- are known to beextremely difficult to control at such low power levels and operating themat that level was something the operators had been specifically warned notto do. No surprise that when the operators did it anyway, they lostcontrol, crashed and burned.

But the consequences of their reactor crashing and burning would not havebeen so severe to anyone but themselves if their reactor had been of adifferent type. The RBMKs were what is called a dual-purpose design. Theycould be configured to produce Plutonium-239 for nukes or to generateelectricity. Although the RBMKs at Chernobyl were configured to produceelectricity, they still couldn't have the containment vessel around thereactor core that almost all other power reactors in the world have,including more recent Soviet designs.

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Most power reactors are run at full power for a year or so and then shutdown, whereupon the containment vessel is opened and a third of the fuel inthe reactor core is replaced. The average fuel element remains in thereactor core for four or five years. When the fuel element goes in, ittypically contains 3 percent Uranium-235, which is the isotope of uraniumthat "burns." And when that spent fuel element is removed, it typicallystill has 1 percent Uranium-235 unburned. But the spent fuel element nowalso has about an equal amount of plutonium that has been produced in theburning of the 2 percent Uranium-235. The plutonium produced, which canalso be burned in a power reactor, can then be recovered via chemicalseparation and incorporated in new fuel elements. This is what they do withspent fuel everywhere else in the world, but because of Jimmy Carter andGreenpeace, we are prohibited from recovering the burnable plutonium fromour spent fuel elements.

Carter and Greenpeace to the contrary, the plutonium produced in anordinary power reactor is not nuke weapon useable. Because the fuelelements are left in the reactor for four or five years, the plutoniumproduced is not pure or even mostly pure Plutonium-239. Plutonium-240 andPlutonium-241 isotopes are also produced, and the longer the fuel elementstays in the reactor core, the more unusable the plutonium recovered fromthe spent fuel is to the nuke weapon designer. For producing pure or nearlypure Plutonium-239 for the nuke designer, the fuel elements should only beleft in the reactor for a few months.

So the RBMKs cannot be operated for a year or so and shut down forrefueling. They are essentially never shut down and every day some of thefuel elements in the core are replaced. Replaced by robots, of course,because the reactor core is highly radioactive when operating, even at zeropower.

What this means is that -- unlike most power reactors -- the RBMKs cannotbe surrounded by a bulletproof, fire and explosion proof, containmentvessel. So when the Unit 4 power plant operators stalled their low and slowreactor, it exploded and burned.

When the water-cooled, graphite-moderated reactor core became uncovered-- losing its coolant -- the core overheated and melted, which a) causedsome of the remaining water in the reactor vessel to disassociate intohydrogen and oxygen, which then exploded like the Hindenberg, blowing theroof off the reactor building, and b) set the graphite moderator in thecore on fire. The contaminated and highly radioactive graphite burnedfuriously, producing dense clouds of radioactive smoke which then went outthe hole in the roof.

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Most of the people who died -- and most of those who received very largedoses of radiation -- at Chernobyl, died trying to put out that fire. Ifthere had been a containment vessel -- which for reasons set forth abovethere couldn't have been -- there still would probably have been anexplosion and fire in the core, but there would have been no hole in theroof and the smoke from the fire could not have spread over Central andEastern Europe.

And, of course, if the operators hadn't been attempting to fly theirre-actor low and slow, none of it would have happened.

Physicist James Gordon Prather has served as a policy implementing official for national security-related technical matters in the Federal Energy Agency, the Energy Research and Development Administration, the Department of Energy, the Office of the Secretary of Defense and the Department of the Army. He also served as legislative assistant for national security affairs to U.S. Sen. Henry Bellmon, R-Okla. Dr. Prather had earlier worked as a nuclear weapons physicist at Lawrence Livermore National Laboratory in California and Sandia National Laboratory in New Mexico.